Chapter 5
Neutron Spectrum
Cheol Ho Pyeon
Abstract The subcritical multiplication factor is considered an important index for
recognizing, in the core, the number of fission neutrons induced by an external
neutron source. In this study, the influences of different external neutron sources on
core characteristics are carefully monitored. Here, the high-energy neutrons generated by the neutron yield at the location of the target are attained by the injection
of 100 MeV protons onto these targets. In actual ADS cores, liquid Pb–Bi has been
selected as a material for the target that generates spallation neutrons and for the
coolant in fast neutron spectrum cores. The neutron spectrum information is acquired
by the foil activation method in the
235 U-fueled and Pb–Bi-zoned fuel region of
the core, modeling the Pb–Bi coolant core locally around the central region. The
neutron spectrum is considered an important parameter for recognizing information
on neutron energy at the target. Also, the neutron spectrum evaluated by reliable
methodologies could contribute to the accurate prediction of reactor physics parameters in the core through numerical simulations of desired precision. In the present
chapter, experimental analyses of high-energy neutrons over 20 MeV are conducted
after adequate preparation of experimental settings.
Keywords Subcritical multiplication factor · Reaction rates · Spectrum index ·
Spallation neutrons
5.1 Subcritical Multiplication Factor
5.1.1 Theoretical Background
In the Accelerator-Driven System (ADS) study on the subcritical system, neutron
multiplication M and subcritical multiplication factor k s [1] are theoretically
expressed with the combined use of total fission reaction rates F in the core (fuel
region) and external neutron source rates S at the target, respectively, as follows:
C. H. Pyeon (B)
Institute for Integrated Radiation and Nuclear Science, Kyoto University, Osaka, Japan
e-mail: pyeon.cheolho.4z@kyoto-u.ac.jp
© The Author(s) 2021
C. H. Pyeon (ed.), Accelerator-Driven System at Kyoto University Critical Assembly,
https://doi.org/10.1007/978-981-16-0344-0_5
125
Neutron Spectrum
Cheol Ho Pyeon
Abstract The subcritical multiplication factor is considered an important index for
recognizing, in the core, the number of fission neutrons induced by an external
neutron source. In this study, the influences of different external neutron sources on
core characteristics are carefully monitored. Here, the high-energy neutrons generated by the neutron yield at the location of the target are attained by the injection
of 100 MeV protons onto these targets. In actual ADS cores, liquid Pb–Bi has been
selected as a material for the target that generates spallation neutrons and for the
coolant in fast neutron spectrum cores. The neutron spectrum information is acquired
by the foil activation method in the
235 U-fueled and Pb–Bi-zoned fuel region of
the core, modeling the Pb–Bi coolant core locally around the central region. The
neutron spectrum is considered an important parameter for recognizing information
on neutron energy at the target. Also, the neutron spectrum evaluated by reliable
methodologies could contribute to the accurate prediction of reactor physics parameters in the core through numerical simulations of desired precision. In the present
chapter, experimental analyses of high-energy neutrons over 20 MeV are conducted
after adequate preparation of experimental settings.
Keywords Subcritical multiplication factor · Reaction rates · Spectrum index ·
Spallation neutrons
5.1 Subcritical Multiplication Factor
5.1.1 Theoretical Background
In the Accelerator-Driven System (ADS) study on the subcritical system, neutron
multiplication M and subcritical multiplication factor k s [1] are theoretically
expressed with the combined use of total fission reaction rates F in the core (fuel
region) and external neutron source rates S at the target, respectively, as follows:
C. H. Pyeon (B)
Institute for Integrated Radiation and Nuclear Science, Kyoto University, Osaka, Japan
e-mail: pyeon.cheolho.4z@kyoto-u.ac.jp
© The Author(s) 2021
C. H. Pyeon (ed.), Accelerator-Driven System at Kyoto University Critical Assembly,
https://doi.org/10.1007/978-981-16-0344-0_5
125